In recent years, attention has been given to an electrically powered vehicle as an environmentally-friendly vehicle, such as a hybrid vehicle, an electric vehicle and a fuel cell vehicle. Such an electrically powered vehicle includes a power storage device formed of a secondary battery and the like, and a motor generator as a traction motor capable of receiving electric power from this electrically powered vehicle to generate driving force. The motor generator generates vehicle driving force at the time of acceleration while carrying out regenerative power generation for converting the kinetic energy of the vehicle into electrical energy at the time of deceleration such as braking. In the electrically powered vehicle, the regenerative power from the motor generator is collected by charging of the power storage device, thereby improving energy efficiency.
On the other hand, excessive regenerative power from the motor generator may cause a problem concerning component protection, such as occurrence of an overvoltage and overcharge of the power storage device. Therefore, control is required to prevent excessive generation of regenerative power from the motor generator.
For example, Japanese Patent Laying-Open No. 2009-219189 (PTL 1) discloses a four-wheel drive vehicle capable of driving the engine by one of front and rear wheels and driving the motor by the other thereof. This four-wheel drive vehicle has a configuration for suppressing and preventing damage to an inverter switching element caused by an overvoltage, when the alternating-current (AC) voltage of the power generator driven by the engine is rectified, converted by the inverter and then applied to the motor.
Specifically, PTL 1 discloses that, when the rollback state of the electric motor for driving a vehicle is detected, the target armature current is set so as to cause flow of the d-axis current not contributing to torque generation, thereby consuming the electric power generated by regeneration of the traction motor. This allows suppression of an increase in the direct-current (DC) link voltage of the inverter that is caused by excessive regenerative power from the traction motor. Consequently, damage to the switching element forming an inverter can be prevented.